This invention relates to the separation of adhered paper from paper-covered gypsum board, and has application in the recovery and recycling of gypsum and paper from paper-covered gypsum board.
In the residential and commercial construction industries, gypsum board with paper adhered to the surfaces thereof (often referred to as gypsum wallboard, or simply wallboard) is an extensively used building material. Generally, it is supplied in the form of large rectangular sheets, which the builder cuts to size depending upon the particular project.
Although efforts may be made to minimize the wastage of material, a single construction site will often generate a substantial amount of leftover gypsum wallboard pieces which are essentially useless and which require disposal. A need for disposal also arises when homes or buildings containing gypsum wallboard are demolished.
Historically, the disposal of wallboard material has posed a problem. At the very least it is an uneconomic nuisance and, in some jurisdictions, it is considered to be an unacceptable environmental hazard. The material is not readily degradable and disposal may be prohibited at conventional dumps or waste fill sites. In some cases, the material is transported by barge and disposed of at sea.
The disposal problem arises because waste wallboard has no significant practical purpose so long as the paper and gypsum board remain adhered together. Further, when exposed to the weather and outside environmental conditions, the combination can deteriorate to a polluting sludge of paper and gypsum. On the other hand, if the paper and the gypsum board are separated, the sludge problem can be avoided. Furthermore, if the separation is sufficiently complete, then the paper and/or the gypsum can be recycled.
Accordingly, efforts have been made to achieve a separation of the adhered paper from scrap wallboard. One such method has involved the pulverization of the wallboard, but the resulting product has been a somewhat inefficient and difficult-to-manage mixture of gypsum board particles and paper fluff. Even so, pulverization is preferable over another known method of using a shredder in conjunction with one-stage or twostage air aspiration to separate paper from non-paper waste; the shredder produces a great deal of fluff and the aspirators are expensive and complicated. As well, it is understood that chemical processes have been tried, but with results considered unsatisfactory either by reason of insufficient separation or excessive cost.
U.S. Pat. No. 5,593,096 is a suggested improved method and apparatus for wallboard recycling wherein the wallboard is hammermilled through holes of a hammermill grate, the hole size being selected to produce a screenable mixture of pieces of paper and separated gypsum particles, which can then in turn be screened to segregate the pieces of paper from the gypsum particles. However, this method and apparatus have a number of disadvantages:
1. Inability to easily separate ferrous materials such as steel from gypsum board prior to hammermilling, resulting in safety and component wear hazards associated with ejection of shrapnel from the hammermill under high force and damage to the hammermill itself.
2. Inability to achieve relatively uniform feed to the hammermill resulting in: (a) the hammermill being plugged with excess gypsum material, thus resulting in poorer separation of gypsum core from the paper, and (b) poorer screening resulting in more paper in the gypsum product and more gypsum in the paper product.
3. Lack of a manual sorting station to supplement screen separation resulting in foreign objects, such as wood, concrete, plastics, aluminum, green waste, putrescible garbage, etc. in the end products and more wear and maintenance to the hammermill.
What is required is a new and improved method and apparatus for separating adhered paper from paper-covered gypsum board. Ideally, the method and apparatus should be able to separate and segregate a substantial amount of adhered paper from paper covered gypsum in a continuous and efficient manner, while minimizing wear and damage to the hammermill or other pulverizer and ensuring safety.
In accordance with a broad aspect of the method of the present invention there is provided a method of separating adhered paper from paper-covered gypsum board, the method comprising the steps of:
(a) Feeding wet and/or dry gypsum board into a feed hopper and onto a conveyor;
(b) Conveying the gypsum board past a magnet to remove ferrous materials prior to being fed into a hammermill or other type of pulverizer;
(c) Fracturing the gypsum board in a hammermill or other type of pulverizer; and
(d) Sieving pulverized gypsum board through at least one screen to segregate paper and gypsum particles.
This method can, if desired, be combined with one or more of the following optional performance enhancing steps:
(a) Prior to conveying the gypsum past the magnet, providing an area wherein non-gypsum debris such as plastic, insulation, wood, concrete, aluminum, green waste, garbage, etc. can be manually sorted and removed from the gypsum;
(b) After sieving pulverized gypsum board through the first screen, resieving the coarsely screened gypsum board through a finer screen to achieve improved gypsum/paper separation; and
(c) Conveying the coarsely sieved and/or finely sieved gypsum past one or more additional magnets to further purify the gypsum product of ferrous debris (e.g. screws, corner bead pieces, nails, etc.).